In modern and future communication systems, location services and location-based services (LCS) are gaining more attention and importance. In order to enable provision of location services and location-based services for terminals in modern and future communication systems, an accurate geographical positioning (hereinafter just ‘positioning’) of the terminals is vital. An accurate positioning is for example particularly valuable in (e.g. VoLTE) emergency use cases, for public safety, for mobile drive tests, under indoor conditions, urban canyons, tunnels, parking halls, subways, vehicles, for mobile drive tests, and the like.
In the framework of 3GPP standardization, LTE control plane signaling support for LCS is introduced from 3GPP Release 9 onwards. Therein, assisted satellite positioning is specified as a primary positioning/localization technique, whilst both a cell ID based positioning and OTDOA-based positioning are specified as fallback positioning/localization techniques in the event that the terminal lacks satellite positioning capability or the assisted satellite positioning fails e.g. due to non-availability of a required number of positioning satellite signals.
The assisted satellite positioning is based on at least four positioning satellite signals of GPS or any other satellite-based positioning system, while the network may provide assistance data for a reliable fix of the position.
The cell ID based positioning and enhancements thereof are based on the fact that the responsible server (e.g. E-SMLC) knows the geographical locations of the cells, that the timing advance can be used to find a terminal's distance from each base station antenna in the vicinity, and that neighbor cell measurements and the like can be used to increase the accuracy of the positioning. That is to say, the consideration of neighbor cells enhances accuracy of positioning.
The OTDOA-based positioning is based on the measurement of an observed time difference of arrival (OTDOA) on the basis of a positioning-related signal. In this regard, a terminal's position can be multi-laterated (typically tri-laterated) with the knowledge of multiple (typically three) base stations' transmit timings and their geographical locations and received time differences of at least two other cells relative to the serving cell of the terminal. In this regard, the terminal detects positioning-related signals from multiple (typically at least three) base stations in the vicinity.
When an increased accuracy of positioning results is desired in a specific communication system, the accuracy of positioning of at least one of the positioning/localization techniques specified for that specific communication system should be improved. The accuracy of positioning of the assisted satellite positioning and the cell ID based positioning may not be easily improved without requiring fundamental changes to the functional and/or structural configuration of the underlying satellite-based positioning system and communication system, respectively. Therefore, when an increased accuracy of positioning results is desired in a 3GPP-based LTE communication system, the accuracy of positioning of the OTDOA-based positioning should preferably be improved.
In this regard, it has conventionally been proposed to measure a receiver path delay which is then taken into consideration for deriving a timing value for the OTDOA-based positioning, thus improving the positioning accuracy. In such conventional techniques, a test or reference signal is typically generated and used for delay measurement on the receiver path, and a relative time difference between this test or reference signal and another signal (e.g. a positioning-related signal, another reference signal, etc.) is determined as an absolute delay value of the receiver path in question.
For example, EP 2 204 664 suggests to measure a relative difference between a reference signal and a delay reference signal, wherein a specific calibration signal or two reference signals are provided to a terminal (including the receiver path in question) by the network, thus requiring the network to provide support for terminal delay measurement. Further, US2004/073392 and JP 2007 096647 A suggest systems where a specific reference signal is created in a device circuitry, which signal is then used for measuring the delay in the receiver path, thus requiring extra hardware (such as a separate signal source, hardware for injecting the signal into the receiver path, etc.) and/or extra power consumption in the device for generating the test or reference signal.
In order to increase accuracy of positioning results, i.e. to improve the positioning accuracy of a timing-based positioning technique (e.g. the OTDOA-based positioning technique), the accuracy of (a measurement of) an underlying timing or timing value at the terminal to be positioned or localized should be improved, preferably whilst avoiding drawbacks of conventional systems, e.g. without requiring network support, extra hardware, extra power consumption, or the like.
Thus, there is a corresponding desire to improve the accuracy of timing and/or timing measurement for a timing-based positioning technique.